For an optical system used with electronic imaging apparatus like digital cameras and digital video cameras, it is now required to have small-format size and optical performance high enough to be well corrected for aberrations. As one approach to achieving size reduction, there has been a bending or flexion optical system known in the art that includes a reflective optical element inside as well as an electronic imaging apparatus incorporating the same.
For the bending optical systems including a reflective optical element, a small-format imaging optical system of positive-negative-positive-positive-negative-positive six-groups construction has been known as set forth in the following patent publications.
JP(A) 2009-69671 has proposed adding and inserting one additional lens group to and into a bending optical system of positive-negative-positive-positive-negative-positive six-groups construction having a zoom ratio of about 7 so that zooming may be implemented on a side where the focal length grows longer than could do at the telephoto end of the six-groups construction, with a zoom ratio of as high as about 10.
JP(A)'s 2009-192771, 2008-225314 and 2008-129238 have come up with a bending optical system of positive-negative-positive-positive-negative-positive six-groups construction with a zoom ratio of 5 to 7.